1. Field of Invention
The present disclosure of invention relates to a liquid crystal display (“LCD”) panel and, in particular, to an improved LCD panel which is capable of inhibiting light leakage around gate lines when using a liquid crystal alignment distribution mode that is intended to provide enhanced side view visibility and to also provide high transmissivity for improving apparent contrast ratio.
2. Description of Related Technology
An LCD device displays a desired image by supplying a video signal to liquid crystal cells arranged in a matrix form and by controlling light transmissivity of the individual liquid crystal cells according to pixel drive signals embedded in the video signal. Optical viewing angle technologies have been developed to solve a viewing angle problem inherent to LCDs wherein appearance of a displayed image might be distorted according to a location from which a viewer watches a screen where the location may be one other than that of a heads on direct facing view of the screen.
The optical viewing angle improving technologies used for LCD devices include a so-called, Patterned-ITO Vertical Alignment (“PVA”) mode, an In-Plane Switching (“IPS”) mode, and a Plane-to-Line Switching (“PLS”) mode.
In the PVA mode, a fringe electric field is generated between a common electrode and a pixel electrode formed respectively in first and second base substrates due to provision of slits in the electrodes. Liquid crystal molecules are symmetrically driven into different orientations on the basis of the placement of the slits and the distributed fringe electric fields generated around the locals of the slits, thereby forming a multi-domain distribution of crystal orientations. In the IPS mode, the liquid crystal molecules are oriented by a lateral electric field formed between a common electrode and a pixel electrode where the latter are both formed to be parallel to each other on a second base substrate. Also in the PLS mode, an insulator is disposed between the common electrode and the pixel electrode in each pixel area. In the PLS mode, an electric field having horizontal and vertical components is generated between the common electrode and the pixel electrode to drive liquid crystal molecules filled between first and second base substrates in each pixel area. In the IPS mode and PLS modes, since the electric field is generated by forming the two electrodes on one same substrate, undesirable image sticking occurs and the light transmissivity is decreased. On the other hand, in the PVA mode, an aperture ratio of each pixel area is comparatively low due to the presence of slits in the common and pixel-electrodes. To solve the above problems, a Dual Field Switching (“DFS”) mode has been recently proposed.
In the proposed DFS mode, liquid crystal molecules are both laterally and vertically aligned with respect to a shaped electric field generated by specially shaped electrode patterns formed on first and second side transparent substrates of the LCD panel. One embodiment of the DFS mode uses a common electrode and a pixel electrode linearly formed in respective planes on the first and second base substrates. The liquid crystal molecules are aligned using a liquid crystal driving electric field in which a lateral (horizontal) portion of the electric field and a vertical portion of the electric field are generated between the common electrode and the pixel electrode in a mixed distributive manner, thereby improving side view visibility and also improving light transmissivity (by keeping the per pixel aperture ratio relatively large). In the DFS mode, since the liquid crystal molecules are driven by electrodes formed over the whole pixel unit area, the transmission area is wide and thus provides good transmissivity. However, the liquid crystal molecules are easily moved by the influence of electric fields from adjacent electrodes (in particular those from adjacent gate lines) and thus it is difficult to prevent extraneous orientations of liquid crystal molecules from being formed about peripheral regions of the different pixel areas.
An LCD panel using a conventional form of the proposed DFS mode suffers from a relatively low contrast ratio when displaying a black or dark gray level since light leakage tends to occur in the vicinity of gate lines due to extraneous orientations of liquid crystal molecules around the gate lines. More specifically, since in the conventional DFS mode, the orientations of liquid crystal molecules in the vicinity of the gate lines are irregularly arranged by the fringe electric fields generated about the gate lines during a horizontal scan interval and these gate line fields are not controllably influenced by the different control voltages being stored on the pixel electrode of the adjoining pixel unit, the irregularly arranged liquid crystal molecules in the area of gate lines are not capable of properly suppressing light transmissivity when a black or dark gray level is desired in the adjoining pixel area, and they thereby can generate light leakage and decrease the apparent contrast ratio of the black or dark gray level in the adjoining pixel area in certain situations so as to give users of the DFS operated panel the impression that the adjoining pixel area is not as dark as it should be. More specifically, although the LCD panel of the DFS mode uses a black matrix in the vicinity of the gate lines for the purpose of blocking light leakage around peripheral edges of each pixel area, the black matrix has a tendency to deviate during mass production from its design-specified normal location due to an arrangement (alignment) error of the first and second base substrates when assembling the LCD panel on a mass production basis. The so-misaligned black matrix is incapable of blocking all the light leakage generated by the liquid crystal molecules adjacent to the gate lines and thus the contrast ratio of the black or dark gray level is disadvantageously decreased when misalignment of the black matrix occurs.